Assessing the role of Antarctic Circumpolar Current strength variability in Antarctic Intermediate Water formation and low-latitude climate over the last 400 ka

The Antarctic Circumpolar Current (ACC) connects all major Ocean basins and plays a pivotal role in regulating ocean circulation modulating the deep-sea ventilation by upwelling and downwelling of water masses. The Southeastern Pacific Ocean (SEP) is a key region of Antarctic Intermediate Water (AAIW) formation, which has significant influence on low latitude climate. South Westerly Winds (SWW) – ACC interaction has an important role in promoting the upwelling of Upper Circumpolar Deep Water (UCDW), which is relatively corrosive and enhances the dissolution of aragonitic foraminiferal tests.  Hence, the percentage abundance ratio of aragonitic test benthic foraminifera Hoeglundina elegans vs total calcareous foraminifera test can serve as a reliable proxy for ACC current strength variability. The upwelling and downwelling of UCDW are responsible for CO₂ release to the atmosphere and oxygen uptake in the AAIW water mass, respectively, affecting the deep sea biota in the SEP. Hence, this study analysed the benthic foraminifera abundance variations in International Ocean Discovery Program (IODP) Site U1542 (~1101 m depth, Chilean margin, under AAIW influence) for the last ~400 ka to evaluate the linkages between ACC, SWW, and AAIW and associated forcing factors. The spectral and continuous wavelet analyses were performed for the AAIW characteristic proxies i.e. oxic species (%), combined suboxic and dysoxic species (%) of benthic foraminifera that show a 44 kyr obliquity cycle. This cycle suggests the influence of Patagonian Ice Sheet (PIS) dynamics and the role of atmospheric CO₂ in regulating marine carbon reservoirs through AAIW production during various glacial-interglacial cycles. The ACC strength variability proxy i.e. aragonitic Hoeglundina elegans (%)/Total calcareous foraminifera (%) shows the presence of ~100 kyr cycle, which is also observed in the Asian monsoon record. This study suggests that ACC has influenced the Asian monsoon by modulating AAIW production, which regulates the atmospheric CO₂ concentration linked with 100 kyr cycle.